Room Temperature Preparation Of The Self-cleaning Nano-TiO₂ Thin Film

At present, the low-temperature preparation and solidifying technology of TiO₂ thin film in our country fall behind in other countries. The industrialization production of self-cleaning thin film has some disadvantages such as complicated technology and too much energy consumption. In this paper, it was improved that TiO₂ thin film technology of Sol-gel method at low temperature, and transparency TiO₂-SiO₂ composite self-cleaning thin films with superior photo-induced property were prepared at room temperature. Films have a good adhesion with substrate.Nano-TiO₂ hydrosols were synthesized using titanium tetrachloride (TiCl4), ammonia (NH3·H2O) and peroxide (H2O2) as raw materials by hydrolyzing, precipitating, peptizing, complexing and refluxing. With the degradation rate of methyl orange as indexes, the process was optimized by orthogonal design. The effect of different parameters on photocatalytic activity of hydrosols was studied. The results show that pH has a significant effect on photocatalytic activity, and the next is refluxing temperature and time. The effect of the volume ratio of TiCl4 and added distilled water is least. Suggested optimum process conditions is as follows: 8 to 9 of pH, 80℃of refluxing temperature, 8 to 10 hours of refluxing time and 1:100 of the volume ratio of TiCl4 and added distilled water.The hydrosols were characterized by X-ray diffraction (XRD), transmitting electron microscope (TEM) and ultraviolet-visible absorption spectra (UV-Vis). The results show that hydrosols contain needle-like nano anatase crystal grains, which grow along the c-axis, with homogeneous morphology, good dispersancy. Absorption edge wavelength of the hydrosols shifts to 470 nm. As the refluxing time lasts and refluxing temperature rises, crystal grain size of the hydrosols grows, but photocatalytic activity enhances in the beginning, and then reduces. TiO₂ hydrosol refluxed at 80℃for 10 h shows the best photocatalytic activity. Under 25 W ultraviolet light irradiation, 60 min degradation rate of 10 mg/l methyl orange is 87.7 %.TiO₂ thin films and TiO₂-SiO₂ composite thin films were prepared by dipping-withdrawing at room temperature. They were characterized by environmental scanning electorn microscope (ESEM), atomic force microscope (AFM), fourier transform infrared spectroscope (FTIR), ultraviolet-visible absorption spectra (UV-Vis) and other means of testing. The results show that there is uniform distribution of particles in the films, which are no holes, no cracks. Grain size of particles in the films is much greater than that in the hydrosols, and morphology has changed from needle-like to approximate sphericity. Transmittance of TiO₂ films is more than 80 % in the visible region. Particles in the films reunion or grow up after the heat treatment, which will have a negative impact on film transmittance, photocatalytic activity and hydrophilic property. In the visible region, transmittance of TiO₂-SiO₂ composite thin films is more than 75 %, and transmittance of the film with 20 % of SiO₂ content (mol %) is nearly 100 %. In TiO₂-SiO₂ films, there are TiO₂ and SiO₂ phase separately, and Ti-O-Si bond, so there are some composite oxides. Films show mountain-range-like structure. Roughness markedly improves with the content of SiO₂ increasing. The more SiO₂, the lower photocatalytic activity of TiO₂-SiO₂ thin films. Thin films with 10 % and 20 % of the SiO₂ content have good super-hydrophilic property. Adhesion of the films and glass substrate enhances greatly by SiO₂ doping.